Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$134.34	13.313%	$152.2247	$152.22	$152.20	$152.20
Purchase #2	$176.90	10.558%	$195.5771	$195.58	$195.60	$195.60
Purchase #3	$15.47	12.731%	$17.4395	$17.44	$17.45	$17.40
Purchase #4	$169.41	9.745%	$185.919	$185.92	$185.90	$185.90
Purchase #5	$55.59	7.630%	$59.8315	$59.83	$59.85	$59.80
Purchase #6	$69.43	4.830%	$72.7835	$72.78	$72.80	$72.80
Purchase #7	$156.76	9.157%	$171.1145	$171.11	$171.10	$171.10
7 purchase totals =	$777.90		$854.8898	$854.88	$854.90	$854.80